1. Field of the Invention
The present invention relates to an intake system of an internal combustion engine including a fuel injection valve for injecting fuel to an intake port of the engine, and an intake air-flow deflection mechanism which serves to deflect flow of intake air so as to produce vortex flow in a cylinder of the engine, and more particularly, to an intake system appropriate for lean-burn operation of an internal combustion engine.
2. Description of the Prior Art
In a conventional intake system of an internal combustion engine, as disclosed in Japanese Patent Unexamined Publication No. 60-230543, flow of intake air is deflected. However, according to the conventional system, strong vortex flow is not produced in a cylinder of the engine because the deflected intake air flow lack orientation or directivity. Further, since fuel is sprayed into the deflected air flow, the direction of injection of the fuel is unfavorably changed so that the fuel cannot be supplied to a target position. Consequently, the fuel sticks to a wall of an intake pipe and flows into the cylinder in the state of liquid, which results in non-uniformity of the fuel-air mixture distribution in the cylinder. Thus, lean-burn operation of the engine cannot be realized.
In view of the above, the present invention aims to prevent non-uniformity of the fuel-air mixture distribution in a cylinder of an internal combustion engine, unlike the prior art, so as to realize uniformity of the distributed fuel-air mixture, and to improve ignitability of the mixture at the time of lean-burn operation of the engine, by selecting the direction of supply of sprayed fuel in order to partially concentrate the mixture flow rich in the fuel in the vicinity of an ignition plug in the cylinder.
Further, the invention aims to prevent the fuel from being blown off by high-velocity air flow for producing tumble flow in the cylinder, which tumble flow accelerates combustion of the mixture in the cylinder.